Effectiveness of positron emission tomography for predicting chemotherapy response in colorectal cancer liver metastases

Hypothesis: Chemotherapeutic agents may be able to convert unresectable colorectal hepatic metastasis to resectable disease, therefore changing the surgical options. The role of positron emission tomography (PET) for patients undergoing chemotherapy remains unclear. We hypothesize that recent chemotherapy treatment could result in false-negative PET results. Design: Case-control study evaluating PET findings. Setting: The University of Texas M. D. Anderson Cancer Center. Patients: From May 1, 2006, through August 31, 2008, data for 224 consecutive patients were entered into a prospective database for evaluation of hepatic metastasis of colorectal carcinoma. One hundred thirty-eight patients underwent PET and conventional imaging (a combination of computed tomography, magnetic resonance imaging, and ultrasonography). All had oncologically sound colorectal operations. Interventions: Liver resection or ablation for colorectal liver metastases. Main Outcome Measures: To determine the accuracy of PET scans to detect residual viable colorectal cancer liver metastases after a significant response to systemic chemotherapy. Results: Patients with biopsy-proven disease under-went hepatic resection (120 patients [87.0%]), radiofrequency ablation (2 [1.4%]), or resection with radiofrequency ablation (7 [5.1%]). Nine patients (6.5%) had inoperable disease that was found intraoperatively. When performed within 4 weeks of chemotherapy, PET had a negative predictive value of 13.3% and a positive predictive value of 94.3%. The sensitivity was 89.9%, the specificity was 22.2%, and the accuracy was 85.5%. Conclusions: Positron emission tomography within 4 weeks of chemotherapy is not a useful test for evaluation of colorectal hepatic metastases. The high rate of false-negative results is likely due to metabolic inhibition caused by chemotherapeutic drugs. We recommend that physicians not use PET in patients recently completing chemotherapy; they should undergo the appropriate oncologic hepatic operation based on the high probability of viable malignant disease.